This invention relates generally to land mobile radios, and more particularly, to a device providing communication between different land mobile radio systems.
Land mobile radios (LMRs) may be used to provide communication between different mobile units. Land mobile radio communication, for example, public safety radio communication (e.g., police, fire department, etc.) is generally available within the VHF, UHF, 700 MHz and 800 MHz frequency bands. Part of each of these frequency bands is allocated by the Federal Communications Commission (FCC) for public safety communication services and are also referred to as Public Safety Frequency Bands. These communications also may be provided using private land mobile radio services (PLMRS).
When LMRs are used, for example, to provide emergency communications, interoperability between different systems (e.g., fire department LMR system and police department LMR system, or different fire department LMR systems) is important. However, each of the different systems may have different communication requirements based on, for example, the manufacturer of the LMR or LMR system and/or the air interface protocol implemented on the system (e.g., trunked or conventional, M/A-COM or Motorola, P25, Enhanced Digital Access Communications System (EDACS), OPENSKY® or Terrestrial Trunked Mobile Radio (TETRA)). Each of these different systems typically include a specific voice encoder (vocoder) and have different encryption schemes. For example, a P25 system typically uses an Improved Multi-Band Excitation (IMBE) vocoder with Data Encryption Standard (DES) or Advanced Encryption Standard (AES) encryption while an OPENSKY® system typically uses an Advanced Multi-Band Excitation (AMBE®) vocoder with AES encryption. Thus, when attempting to communicate between different LMR systems, not only is interoperability an issue, including end-to-end security and encryption, but also minimizing voice quality degradation.
Known systems use analog voice communication as the interface between two disparate LMR systems. Accordingly, a digital audio source from one system is decrypted and de-vocoded. The resulting analog audio is then re-vocoded and re-encrypted for transmission to the other LMR system. Further, end-to-end encryption is only implemented between devices using the same vocoder, encryption algorithm and encryption key. Additionally, in some wide-area digital LMR systems such as state-wide systems, for efficiency of RF coverage, different system types may be used in different parts of the communication coverage area where users may roam. These systems are sometime referred to as hybrid systems. In such systems, different users within the same organization may use different types of communication protocols with different vocoders and encryption algorithms. Accordingly, depending on the area in which a user is communicating, the same radio may be forced to switch between different system types. Therefore, interoperability may be needed not only between systems using different communication protocols and operated by different entities, but within a single system wherein different communication protocols are used.
Thus, these known systems add significant complexity in system design and control, thereby adding cost. There is also the potential for significant audio quality degradation between the two systems. Further, the intercommunication is typically limited in flexibility and often includes at some point in the communication link a clear unencrypted voice audio transmission. This unencrypted transmission between the two LMR systems results in a less secure communication connection.